This invention relates to a method and apparatus for scanning an object by using the light, for use in a picture reproducing machine such as a color scanner and a laser reproducing apparatus for plate making.
In a conventional picture reproducing machine such as a color scanner and a laser reproducing apparatus for plate making, the scanning of a picture image is carried out for recording it on a photosensitive material by a flat or cylindrical scanning method wherein the photosensitive material is mounted to a flat or cylindrical surface. The cylindrical scanning method is less operative than the flat scanning method, for example, the mount or the demount of the photosensitive material is rather troublesome. However, since the angular speed of scanning is uniform, the reproducibility of the picture is accurate and thus no particular correction lens system is required. Accordingly, its optical system is simple and its producing cost is low.
In the cylindrical scanning method for recording the picture image on the photosensitive material, an outer cylindrical surface scanning method or an inner cylindrical surface scanning method is employed, the former being largely used in the color scanner and the color facsimile for plate making. In the former method, since the cylinder on which the photosensitive material is mounted is rotated, the scanning speed is restricted to be a low speed, and, when the scanning is forcibly carried out at a high speed, the material mounted to the outer surface of the cylinder is often flown off by the centrifugal force.
Meanwhile, in a conventional inner cylindrical surface scanning method, the photosensitive material mounted to the inner cylindrical surface of the cylinder fixed is scanned by a light beam reflected by a cutoff mirror having a reflecting surface at an angle 45.degree. with respect to a central axis of the cylinder or a pyramid mirror having a plurality of such reflecting surfaces at the angle 45.degree., while the cutoff mirror or the pyramid mirror is rotated, it reflecting the light beam incident thereto from the direction along the central axis of the cylinder. In this embodiment, because there is no need to rotate the cylinder, which is different from the outer cylindrical surface scanning method, the scanning speed can greatly be increased, whereas it is difficult to attach the material to be scanned onto the inner cylindrical surface of the cylinder. When the photosensitive material is scanned by a plurality of light beams in the same time, each light beam should be incident on the material at an angle perpendicular to the scanning direction, and in order to obtain such a condition a correction optical system is required. Therefore, it difficult to realize this method.